Catheters are small pipes or tubes of various diameters which may be inserted into the particular body cavity to be treated. So-called balloon catheters, which are used above all to expand or reopen a vessel in angioplasty, have a guide wire which is first inserted into the vessel to be treated. A tube which has a non-dilated, folded balloon in a predefined area of the tube is then advanced along the guide wire up to the location of the vessel to be treated so that the balloon is placed in the area of the location of the vessel to be treated, which has a stenosis, for example. The balloon is then dilated, i.e., unfolded and expanded, so that the location to be treated is reopened or expanded and the flow of the bodily fluid in the vessel is no longer obstructed or is no longer obstructed to the previous extent. Finally, the balloon is deflated and removed from the vessel along the guide wire. The guide wire is also retracted from the vessel simultaneously or subsequently.
To achieve optimum properties in regard to flexibility and pushability, catheters currently being used frequently have an internal tube and an external tube which at least partially encloses the internal tube. For purposes of the present disclosure, the term “pushability” means the property of a catheter to transmit longitudinal forces from the proximal end of the catheter to its distal end without forming kinks. Internal and external tubes comprise identical or different materials, such as a polyamide. The balloon of the catheter is connected to the distal end of the external tube, in particular, the balloon is welded thereon.
Balloon catheters are frequently used not only for dilation of a vessel but also for the purpose of introducing intraluminal endoprostheses at a location to be treated in a body cavity. For this purpose, the balloon of a catheter of this type has an endoprosthesis section which is used for positioning an intraluminal endoprosthesis. The endoprosthesis section is the cylindrical section of the balloon, which does not have to be longer than the endoprosthesis. This section is possibly somewhat longer, but only slightly, than the endoprosthesis. The intraluminal endoprosthesis, preferably a stent, is crimped onto the balloon of the catheter in this section and inserted as a system therewith jointly into the body cavity. When the endoprosthesis has reached the intended location after the insertion, the endoprosthesis is expanded together with the balloon of the catheter and remains in the treated vessel after the deflating and folding of the balloon.
Intraluminal endoprostheses, preferably in the form of stents, are currently widely used because intraluminal endoprostheses allow a simple and cost effective treatment for vascular illnesses. Intraluminal endoprostheses frequently have a tubular or hollow-cylindrical main lattice which is open on both longitudinal ends. The main lattice of an endoprosthesis of this type is inserted using a catheter into the body cavity to be treated and is used after removal of the catheter for supporting the body cavity. Constricted areas in the vessels may be expanded permanently or at least over a specific period of time by the use of stents, so that an increase of lumen in the body cavity results.
Intraluminal endoprostheses are frequently also provided with pharmaceutically active substances which are released over a specific period of time in the organism.
These pharmaceutically active substances may be used, for example, for preventing restenosis or agglomerations. It is possible through the release of pharmaceutically active substances with which intraluminal endoprostheses of this type are provided to perform only a local treatment, i.e., an elution of an active ingredient essentially only in the tissue surrounding the intraluminal endoprosthesis. This procedure is also referred to as “local drug delivery” (LDD). The treatment location at which the active ingredient is to unfold its pharmacological effect directly adjoins the location of the implantation of the intraluminal endoprosthesis.
For purposes of the present disclosure, a “pharmaceutically active substance” (or therapeutically active or active substance) means a vegetable, animal, or synthetic active ingredient (medication) or a hormone which is used in suitable dosing as a therapeutic agent for influencing states or functions of the body as a replacement for natural active ingredients produced by the human or animal body, such as insulin, and for removing or making harmless pathogens, tumors, cancer cells, or materials foreign to the body. The release of the substance in the surroundings of the endoprosthesis has a positive effect on the course of healing or counteracts pathological changes of the tissue as a result of the surgical intervention and/or is used to make diseased cells harmless in oncology.
For example, pharmaceutically active substances of this type have an anti-inflammatory and/or antiproliferative and/or spasmolytic effect by which restenosis, inflammations, or (vascular) spasms may be avoided, for example. Substances of this type may comprise, in especially preferred exemplary embodiments, one or more substances of the active ingredient groups of calcium channel blockers, lipid regulators (such as fibrates), immunosuppressive agents, calcineurin inhibitors (such as tacrolimus), antiphlogistics (such as cortisone or diclofenac), anti-inflammatory agents (such as imidazoles), antiallergy agents, oligonucleotides (such as dODN), estrogens (such as genistein), endothelium producers (such as fibrin), steroids, proteins, hormones, insulins, cytostatics, peptides, vasodilators (such as sartanes), and agents having an antiproliferative effect, such as paclitaxel or sirolimus.
Currently, intraluminal endoprostheses which comprise a material subject to biodegradation are also used. For purposes of the present disclosure, biodegradation mean hydrolytic, enzymatic, or other metabolically-related degradation processes in the living organism which are caused by the bodily fluids coming into contact with the endoprosthesis and result in gradual dissolving of at least large parts of the endoprosthesis. For purposes of the present disclosure, the term biocorrosion is frequently used synonymously with the term biodegradation. For purposes of the present disclosure, the term bioresorption comprises the subsequent resorption of the degradation products by the living organism. Biodegradable materials of this type may be implemented from polymers or metals. In connection with stents, the abbreviation “AMS” (absorbable metal stent) is also common. Stents of this type contain a biodegradable metal, preferably magnesium and/or a magnesium alloy.
In addition, providing intraluminal endoprostheses with functional elements, which have a different material composition in comparison to the material of the main lattice in at least a part of their volume, is known. These functional elements are used to determine the position of an endoprosthesis in the body or to release medications, for example.
The ascertainment of the position of an endoprosthesis is frequently performed using imaging methods, for example, using an x-ray radiation device. Because the materials employed for the main lattice of endoprostheses of this type typically only absorb x-ray radiation to a small extent, i.e., are x-ray translucent or radiolucent, the endoprostheses are frequently provided with so-called x-ray markers which contain a material which has a higher absorption of the x-ray radiation (x-ray opaque or radioopaque material).
In a catheter which is used to introduce an intraluminal endoprosthesis, such as a stent, the problem frequently exists that rigidity jumps arise on the ends of a stent attached to such a catheter. In particular, if the stent is rigid or has a high rigidity due to a large crimping diameter, the danger exists that the catheter will be kinked at the rigidity jumps in curves of the body cavity which the catheter passes and thus jam the guide wire. The friction between catheter and guide wire may thus increase. If the stent additionally has x-ray markers on the stent ends, the danger exists that the x-ray markers will protrude in curves due to the kinking of the catheter and thus will remain hanging in the body cavity or on the guide catheter.
A balloon catheter is disclosed in U.S. Pat. No. 7,022,106, in which an increase of the feed force which is transmitted by the external tube to the distal end of the catheter is achieved. For this purpose, the known catheter has an external tube and an internal tube which extends coaxially in the external tube. In addition, a balloon is situated in proximity to the distal end of the catheter. The balloon is fastened at its proximal fastening point to the external tube and is connected to the internal tube at its distal fastening point. Moreover, the external tube may be reinforced to increase its rigidity and pushability along this segment of the catheter. In one exemplary embodiment of the known catheter, the external tube tapers step-by-step starting from the proximal fastening point in the distal direction and forms a conical section. The disadvantage of this known catheter is that the construction has a design which is quite complicated, making the catheter costly to produce. In addition, the known catheter does not solve the problem described above because the rigidity jumps at the stent ends are not remedied by the known design.
A further known catheter is described in U.S. Patent Publication No. 2007/0016132. This catheter has an oblong body having a proximal section and a distal section. Furthermore, a plurality of stiffening means are provided on the catheter which are used to vary the rigidity along the catheter body. Various types of stiffening means are explained in the publication which overlap or have a varying rigidity along the length of the catheter body, for example. For this purpose, the stiffening means situated along the length of the body of the catheter may comprise various materials which have a varying flexibility. However, the publication does not concern itself with the problem of the rigidity jumps at the endoprosthesis ends when an intraluminal endoprosthesis is introduced into a body cavity using the catheter.